Material guide
FFKM O-Rings: When Perfluoroelastomer Is Worth It
Perfluoroelastomer O-rings for chemical, high-temperature and semiconductor service: where they fit, how they compare with FKM, EPDM and the alternatives, and how to specify one.
FFKM (perfluoroelastomer) is the O-ring material to specify when nothing else survives the media: aggressive chemicals, hot amines and ketones, steam, high vacuum and plasma service. The Parker O-Ring Handbook (ORD 5700) rates the general class for continuous service from -26 C (-15 F) to 320 C (608 F); named brand grade sheets run to 327 C (621 F) at the top and -42 C (-44 F) at the cold end. It behaves like a rubber seal while resisting chemicals almost the way PTFE does. It also costs far more than the common elastomers, so it earns its place only where Viton® (FKM) or EPDM would fail. This guide covers where FFKM fits, how it compares with the alternatives, and what an RFQ needs to say.
What is FFKM, and how is it different from FKM?
Both are fluorinated rubbers, and the names are one letter apart, which causes real ordering mistakes. Under ASTM D1418, FKM is the fluoroelastomer family (Viton is one polymer maker's brand of FKM) and FFKM is the perfluoroelastomer family, in which every hydrogen on the polymer backbone has been replaced with fluorine. That full fluorination is what gives FFKM chemical resistance close to PTFE. Kalrez® (Qnity, formerly DuPont), Chemraz® (Greene Tweed) and Parofluor® (Parker) are all FFKM brands; see the branded vs generic FFKM guide for how the brands compare. The aerospace material specification for perfluoroelastomer O-rings is AMS 7257; a print that cites it wants a compound qualified to that document.
When does an application need FFKM?
The decision is media first, temperature second. The table below follows the compatibility notes in the Parker O-Ring Handbook (ORD 5700).
| Situation | Why FKM or EPDM fails | FFKM answer |
|---|---|---|
| Ketones (acetone, MEK) and amines | Acetone and MEK swell FKM heavily; amines attack it. EPDM tolerates ketones but not the oils usually present in the same system | Near-universal resistance, ketones and amines included |
| Hot steam and hot water | Standard FKM degrades in steam; EPDM handles steam but not petroleum oils | Steam-rated FFKM grades handle both in one seal |
| Mixed aggressive streams (acids plus solvents plus heat) | No single FKM or EPDM compound covers the whole list | One compound covers the list |
| Semiconductor wet, plasma and CVD chambers | Extractables and particle shedding from filled compounds contaminate the process | Ultra-pure and plasma-resistant FFKM grades |
| Continuous service above about 204 C (400 F) | Above the FKM continuous ceiling in the Parker table | Standard FFKM to 320 C; high-temperature grades higher per the grade sheet |
| High vacuum with chemical exposure | Outgassing and swell in ordinary compounds | Low-outgassing FFKM grades |
| Fluorinated refrigerants (R11, R12, R13) | Not an FKM or EPDM problem | The one recognized FFKM weak spot; use neoprene or another compound |
FFKM temperature range and properties
The ranges below are the published Parker handbook figures; individual grade sheets extend the top end and the low end, and the grade sheet governs.
| Property | Typical value | Source and note |
|---|---|---|
| Continuous service temperature, general class | -26 C to 320 C (-15 F to 608 F) | Parker ORD 5700 compound table |
| Select high-temperature grades | up to 320 C (608 F) | Parker ORD 5700; grade sheets to 327 C (621 F); the grade sheet governs |
| Low-temperature grades | down to -42 C (-44 F) | Kalrez 0040 grade sheet (Kalrez CPI selector guide); deep cold is not an FFKM strength |
| Chemical resistance | Aromatics, ketones, amines, acids, bases, steam, vacuum | Parker ORD 5700; exception: fluorinated refrigerants |
| Standard durometer | 75 Shore A; 90 Shore A grades for high pressure | Manufacturer grade lists; see the durometer guide |
| Material designation | FFKM under ASTM D1418; aerospace O-rings to AMS 7257 | ASTM and SAE designations |
| Common brands | Kalrez, Chemraz, Parofluor, plus value-tier lines | Owners named in the trademark line below |
| Form | Branded lines are sold as finished parts by their owners; generic FFKM is molded from purchased polymer | Manufacturer distribution model |
How does FFKM compare with the alternatives?
Before an FFKM quote goes out it is worth checking whether a less exotic compound covers the media. The temperature figures are the Parker O-Ring Handbook ranges; a PTFE-encapsulated ring has no single range, because its jacket and core sheets govern.
| Material | Continuous range (Parker handbook) | Where it beats FFKM | Where it loses |
|---|---|---|---|
| FKM (Viton) | -26 C to 204 C (-15 F to 400 F) | Oils, fuels, aromatics, chlorinated solvents at far lower cost | Ketones, amines, hot water and steam, brake fluid |
| EPDM | -57 C to 150 C (-70 F to 302 F); steam compounds to 204 C | Steam, hot water, brake fluid, ketones, acids | Every petroleum oil and fuel |
| Aflas® (FEPM) | -9 C to 232 C (16 F to 450 F) | Sour gas, amines, steam where FKM fails | Narrower chemical list than FFKM; low-temperature flexibility |
| PTFE-encapsulated O-ring | No single range applies to an encapsulated ring; the jacket and core sheets govern. | PTFE inertness at a fraction of FFKM cost | Static or slow service only; no elastic memory after compression |
| Silicone (VMQ) | -54 C to 204 C (-65 F to 400 F) | Dry heat and extreme cold | Fuels, steam, dynamic service |
| FFKM | -26 C to 320 C (-15 F to 608 F); named grades to 327 C and -42 C on their makers' sheets | The everything-else case | Fluorinated refrigerants; deep cold; cost |
The FFKM vs FKM comparison walks the FKM decision in detail, and the temperature range guide lists every material.
Which FFKM grade?
Grades within one brand are tuned for different service, and the grade number on the print matters more than the brand name. The families every maker offers, in the manufacturers' own terms: a general-purpose chemical-processing grade, a steam and hot-water grade, a high-temperature grade that is usually not steam-rated, a 90 Shore A grade for high pressure and rapid gas decompression, a low-temperature grade, and a semiconductor lineup of ultra-pure and plasma-resistant grades. The branded vs generic FFKM guide lists the grade numbers by brand.
How to specify an FFKM O-ring
Give the AS568 dash size or the measured inside diameter and cross-section (the AS568 size chart and the dash number guide cover the size system), the media and its concentration, the continuous and peak temperatures, the pressure, and whether the seal is static or dynamic. Your engineering names the grade from the media: general chemical service, steam service, high temperature, plasma or ultra-pure. If the print says "Kalrez or equal", the equal is the print owner's decision: name the grade your engineering approved and it is quoted with the maker's sheet; a grade number with no "or equal" is quoted as named. Durometer is normally 75 Shore A; 90 Shore A grades exist for high pressure and rapid gas decompression. Because the branded lines are sold as finished parts, a non-standard size means a molded special from the brand owner rather than a cut from cord stock.
Viton is a trademark of The Chemours Company; Kalrez is a trademark of Qnity Electronics; Chemraz is a trademark of Greene Tweed; Parofluor is a trademark of Parker Hannifin; Aflas is a trademark of AGC. No affiliation or endorsement is implied.
Sources
- Parker O-Ring Handbook ORD 5700, service temperature table, page 7-2 (FFKM -26 C to 320 C), read 2026-09-25
- Parker O-Ring Handbook ORD 5700, section 2.2, read 2026-09-14
- Parker O-Ring Handbook ORD 5700, sections 2.2.10 (FFKM) and 2.2.14 (FEPM), read 2026-09-14
- Kalrez CPI Product Selector Guide KZE-A40126, Qnity Electronics, November 2022, read 2026-09-14
- AMS 7257
- AS568
- ASTM D1418
Reviewed by Grant Midstokke, Conquest Seal Corporation. Last updated September 2026. Spec values in this guide are drawn from the sources named in the sentence where each appears; the compound datasheet and your application conditions govern the final choice.
Frequently asked questions
Is FFKM the same as Kalrez?
No. Kalrez is one manufacturer's trademark for its FFKM line. Chemraz, Parofluor and several other lines are the same polymer family. A print that says FFKM accepts any of them; a print that names Kalrez and a grade number is asking for that grade.
Can FFKM replace Viton everywhere?
Chemically it could, but it costs far more and its low-temperature flexibility is worse than a special low-temperature FKM. Use FFKM where FKM is known to fail: ketones, amines, steam, high vacuum and temperatures above the FKM ceiling.
What is the one thing FFKM does not resist?
Fluorinated refrigerants such as R11, R12 and R13, per the Parker handbook compatibility notes. Neoprene (CR) is the usual choice there.
Does FFKM need a special groove?
No. FFKM O-rings use standard AS568 sizes and standard gland dimensions; the groove design guide applies. Its compression set at high temperature is better than FKM, which is one reason it holds a seal longer in hot service.
Is FFKM available FDA compliant or USP Class VI?
Specific grades are offered by their makers with FDA 21 CFR 177.2600 compliance or USP Class VI test reports, typically for pharmaceutical processing. Compliance belongs to the grade, not the polymer family; see the FDA and food-grade O-rings guide.
Which hardness should an FFKM O-ring be?
75 Shore A is the common grade, and Conquest's legacy compound chart lists a 75 A grade against AMS 7257; 70 A is offered for softer sealing at low pressure and 90 A where pressure or clearance drives extrusion. Each grade's own sheet gives its temperature range.
What do the cold limits mean in practice?
The Parker handbook's service temperature table (page 7-2) puts the class at -26 C, and low-temperature grade sheets run to -42 C (Kalrez 0040). Below that the ring stiffens and stops following the gland, so a cold-start service usually wants a low-temperature grade named on the print or a different material.
Is FFKM available in metric sizes?
Yes. Perfluoroelastomer is molded to the ISO 3601 metric list as well as the AS568 inch list, and the five metric cords (1.8, 2.65, 3.55, 5.3 and 7.0 mm) sit inside the AS568 cross-section bands, so a metric groove can often take an AS568 ring of matching inside diameter when the print allows it. Send both the callout and the groove dimensions when a metric drawing meets an inch stock list.
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